As above, it depends on what you specialise in. As you'll see on the site or in the prospectus, the Natural Sciences degree branches out at stage 2 into a choice between Physics, Chemistry, Biology, Earth Science, Environmental Science, and Planetary Science. It also has a generalist option but I wouldn't recommend that. Basically how it works is that you would then study modules in that subject and your final degree will have that subject in its name, e.g. Natural Sciences (Biology). You would then be able to use that degree in the same way you would a Biology degree. The same with physics, chemistry, etc.
So your options at masters, PhD, in your career, etc. essentially rely on what you specialise in. It's also worth keeping in mind that if you want to study Physics or Planetary Science you need to study Essential Mathematics 1 (MST124) at stage 1. If you're not sure what to specialise in then I'd recommend doing MST124 since it opens up those options. I often hear that Chemistry has very good job prospects if that means much to you, but any degree in science shows a high level of numeracy, analytical ability, etc. which are valuable skills in most careers.
You should also check out Mathematics and Physics if you're planning on studying physics or planetary science. You can study most of the modules from those in addition to advanced mathematical modules, giving you accreditation by both the Institute of Mathematics and its Applications (IMA) and the Institute of Physics (IOP). It involves a mixture of Applied Mathematics modules and Physics modules. These include options in astrophysics, which makes it similar to planetary science if you want it to be.
There are also other science degrees such as Environmental Science, which is similar to Natural Sciences (Environmental Science) but requires travelling to do practical experiments, whereas the Natural Sciences version does this virtually. There is also Health Sciences, which essentially splits your modules between Biology and Psychology. I'd recommend checking out all of the various more specialised science degrees, although Natural Sciences is the most flexible by far.
Good luck!